The present invention relates to a composition and a method of preparing porous silica compositions with uniform and controlled pore sizes.
In the past, there have been difficulties in making silica bodies which are porous and uniform in size. One technique used in the industry is to incorporate certain metal oxides within a silica network. Typically an aqueous solution is prepared from silica solutions, as alkali metal silicates, quaternary ammonium silicate, colloidal silica, and mixtures thereof. A metal oxide is then added to the silicate solution and an organic gelating agent is added to cause polymerization of the silica to a coherent and porous body. The metal oxide becomes part of the silica network. Although porous silica bodies are obtained by this preparative technique, the size of the pores throughout the bodies are not uniform. Thus, the technique is not very desirable.
There are techniques practiced in the art which do produce porous silica compositions that have uniform pore sizes, but the techniques are limited by such variables as ratio of alkali metal silicate to colloidal silica solutions, the concentration of silica, the amount of dispersion employed and the like. Other difficulties with the techniques practiced in the art are obtaining acceptable pore size distributions of the polymers and controlling polymerization. One technique in the art is to prepare porous bodies from solutions containing a soluble alkali metal silicate, a potassium silicate, colloidal silica and a gelating agent.
A severe limitation in using this technique is that the spheres can only be successfully made from potassium silicates. Potassium silicates are expensive and are not readily available. When sodium silicates are used with the colloidal silicates, the solution immediately gels. The principle problem is that the colloidal silica and the sodium silicate are incompatible when admixed together. Thus, due to the immediate gelling of the solution, acceptable polymerizing of uniform spheres from sodium silicates is not possible.
Thus, it would be desirable to have more flexibility in the concentrations, types of silicate used and to be able to produce silica bodies with uniform pore diameter distribution. A method of preparing a porous silica composition from a sodium silica/-colloidal silica combination would be desirable, since sodium silicates are inexpensive and are readily available.